Formatter: Add EmptyWithDanglingComments helper (#5951)

**Summary** Add a `EmptyWithDanglingComments` format helper that formats
comments inside empty parentheses, brackets or curly braces. Previously,
this was implemented separately, and partially incorrectly, for each use
case.

Empty `()`, `[]` and `{}` are special because there can be dangling
comments, and they can be in
two positions:
```python
x = [  # end-of-line
    # own line
]
```
These comments are dangling because they can't be assigned to any
element inside as they would
in all other cases.

**Test Plan** Added a regression test.

145 (from previously 149) instances of unstable formatting remaining.

```
$ cargo run --bin ruff_dev --release -- format-dev --stability-check --error-file formatter-ecosystem-errors.txt --multi-project target/checkouts > formatter-ecosystem-progress.txt
$ rg "Unstable formatting" target/formatter-ecosystem-errors.txt | wc -l
145
```

crates/ruff_python_formatter/tests/snapshots/format@expression__dict.py.snap

@@ -62,6 +62,9 @@ a = {
     # comment
     3: True,
 }
+
+x={  # dangling end of line comment
+}
 ```
 
 ## Output
@@ -126,6 +129,9 @@ a = {
     # comment
     3: True,
 }
+
+x = {  # dangling end of line comment
+}
 ```
 
 

crates/ruff_python_formatter/tests/snapshots/format@statement__delete.py.snap

@@ -76,6 +76,9 @@ del (
     # Deleted
 )  # Completed
 # Done
+
+del (  # dangling end of line comment
+)
 ```
 
 ## Output
@@ -211,6 +214,9 @@ del (
     # Deleted
 )  # Completed
 # Done
+
+del (  # dangling end of line comment
+)
 ```